The goal of this National Research Service Award (F32) is to prepare Tricia Leahey to become an independent scientist studying innovative behavioral approaches for the treatment of obesity. Through a combination of didactic and direct mentored training experiences, this training plan will provide her with skills and knowledge in the following areas: the epidemiology, health consequences, and assessment, treatment and prevention of obesity;the methodology, statistics, and ethics of clinical research in obesity;and the effects of social comparison processes on weight control. Tricia Leahey will work closely with her mentor, Dr. Rena Wing, throughout the course of the award. The resources at The Miriam Hospital/Warren Alpert Medical School of Brown University combined with the expertise of her mentor will provide Tricia Leahey with the ideal environment to achieve her long-term goals. Obesity is a major public health problem. Group behavioral weight loss programs are the treatment of choice for moderately overweight and obese individuals. While these interventions are delivered in group format, and social factors are known to influence weight loss in such programs, no one has ever examined the effects of interpersonal interactions among group members on weight loss. Health promotion interventions have identified that comparison of progress amongst group members predicts outcome and maintenance of health behavior;however, no one has ever examined the effects of social comparisons among group members in a behavioral weight loss intervention. Furthermore, no one has ever tried to modify the comparison process to enhance intervention outcome. As such, the aims of this application are to (1) identify social comparison processes that predict weight loss in a group behavioral weight loss program and (2) using the information obtained from Study I, develop a social comparison weight loss intervention and implement a randomized controlled trial to test this intervention. Two studies are proposed. Study I will be a group standard behavioral weight loss program in which social comparison processes will be measured and used to predict weight loss. Study II will be a randomized clinical trial in which participants will be assigned to receive 6 months of a standard behavioral weight loss program or a standard behavioral treatment plus social comparison intervention. This study will determine whether the social comparison intervention can effectively increase social comparisons processes identified to predict weight loss in Study I. The long term goal of this research is to enhance group behavioral weight loss and weight loss maintenance programs by promoting social comparison processes associated with weight control.